Use the slnc (silence) embedded speech command. You can add an arbitrary amount of silence anywhere in the text by inserting the [[slnc x]] command (where x is a number of milliseconds). For example, inserting extra silence between the items in a list makes it easier for people to take note of each item. Listen to the following sentence, which lists four items, separated by commas:
Don't forget to bring your hat, sunglasses, sandals, and towel.
Now listen to the same sentence, with 400 milliseconds of silence inserted between the listed items, and notice that you hear each item more distinctly:
Don't forget to bring your hat, [[slnc 400]] sunglasses, [[slnc 400]] sandals, [[slnc 400]] and towel.